Two-cycle engine scavenging and charging



Nov. 6, 1934. E. B. PoLLlsTER 1,979,770

TWO-CYCLE ENG-INE SAVENGING AND CHARGING Filed Oct. '7, 1931 lll I M INVEIQOR. ...KAV 'im l W my l BY n onirica TWO-CYCLE ENGINE SCAVENGING AND CHARGHNG Edward B. Pollister, St. Louis, Mo., assigner to Busch-Sulzer Bros-Diesel Engine Company, St. Louis, M0., a corporation of Missouri Application October 7, 1931, Serial No. 567,347

9 Claims. (Cl. 12S- 65) My invention relates to two-cycle internal corndegree of load or speed for which the lower preshustion engines having piston-controlled scavsure source or sources will serve is chosen from enging-air and exhaust ports, and more particthe standpoint of economy. The higher-pressure ularly to injection type engines of this customary source or sources is designed to be adequate to form, that is to say, Diesel engines in which the supply the engine needs at higher loads or speeds so fuel is introduced at or about compression dead when used jointly with the lower-pressure source center. or sources. Then at the higher loads, and espe- More particularly, my invention relates to encia-ily at the higher speeds, and where supergines of the kind indicated which are required charging is required. I employ the scavenging and 10 to operate under loads that vary widely from time Charging pl'oCSSS above outlinedy using, When 65 to tinie, and especially engines of this kind that doing so, the separate sources for the high and are required to operate at diierent speeds, such the low pressure airs as stated, resulting in sulo-,- as marine engines.` stantial operating economy in the power con-V AS appears in @O pending applications, 1 have suined compressing the scavenging kand cornl discovered that better scavenging than heretobustion air under these conditions. But at lower 70,

fore, and improved charging and stipsi-Charging, loads, where less combustion air will serve, and of engines of the kind indicated, are obtainable at the lower speeds, when the air admission by the joint use of high and low pressure air periods are of relatively long duration, this inwhere the low-pressure air is admitted as and Voniion diSooutilluoS ibo higher-DroSSuio ai?,

202 while the exhaust port is open and the admission using thon only the lower-DreSSuro Source or 75 of the high-pressure air is begun early, at the sources alone; and profoably, instead 0f Simply very instant the pressure within the cylinder has discontinuing or cutting out the higher-pressure fallen suiiciently to receive it. Ihave discovered Souroe from Sorvoo, I 'Ghrl Ciieoi the loWolals@ that such process is particularly desirable for pressure air into the engine cylinder 0r Cylinders i injection type engines which operate at such high through the ilgh-DTSSSLH'G puSSage or paSsageS 30 speeds thatthe periods available for air admisas well as through the 10W lofoSSule passage 01 sion are too short for adequate scavenging and passages, 'BhuS making use 0f the high-preSSuTe charging by the simpler scavenging and charging passages to secure adequate scavenging and process heretofore employed, and especially is charging, or some superchargingii desired. Thus well adapted for Diesel engines designed for oper- I secure economical and convenient operation 85 ation at higher speeds than usual for Diesel under those operating conditions which do not engines, say ,from 400 to 1000 R. P. M., and require the extra high air pressure, as well as wherein it is desirable to eliminate all valve gearunder those conditions for which the extra high` ing in the vicinity of the scavenging and chargpressure is desirable.

mg pay-tg From one aspect the object 0f my As will loe understood from the foregoing, some 90 present invention is to apply, in an economical convenient means must loe included for stopping manner, this scavenging and charging or super- (and starting again) the supply of higher-pres-v charging process to enginesof the kind indicatedr sure air at the proper times, and this without which are required to operate under-widely varystopping the lower-pressure source or sources.

ing load conditions, and especially to engines By preference, I employ for this purpose an au- 95 Y which are called on to operate at times at high tomatic or self-operating valve or valves (i. e., speeds and at other times at low` speeds; more a valve or valves opened and closed by a diierspecically, to apply such alprocess to such enence between the gas pressures on its opposite gines in a manner which is economical of the sides) for controlling the communication between .45 power required for providing the scavenging and the low-pressure source or sources and the high- 100 Charging 0I' Supel'ohl'gilg air. pressure passage or passages (preferably a pas- To this end I employ separate sources for the sage between the high and lower pressure receivhigh and low pressure air. For the source or ers), and also, when necessary (as will usually sources oi low pressure air, I employ apparatus be the case), for closing and opening the concapable of` supplying an adequate volume of air neetion from the higher-pressure receiver to the 105 ai adequate loToSSU-fo to Satisfy the needs of the higher-pressure air source or sources, when the engine at sonie degree of load or speed less than higher-pressure source is taken out of and is rethe maximum, and capable of supplying such turned to action. needs throughout a certain range of load or speed An embodiment of my invention is illustrated variation less than the maximum; the highest diagrammatically in the accompanying drawing, 110

Figure 1 being an elevation, partly in section, of one cylinder and the adjacent portion of the air receivers of a multiple cylinder Diesel engine, its sources of air being also indicated, Figure 2 being a sectional view substantially on the line II-II of Fig. 1, the head of the piston being shown in elevation, and Fig. 3 being a section on line III-III of Fig. 1.

In the drawing the engine cylinder l, its piston 2, piston-controlled exhaust ports 3, and two tiers of air inlet ports 4 and 5 will be recognized. The element at 12 will serve to represent fuel injection means whereby fuel is injected into the cylinder at about the end of each compression stroke as usual. The exhaust'ports 3 and air inlet ports 4 are placed substantially as in ordinary twocycle Diesel engines scavenged and charged by low pressure air, that is to say, the exhaust ports 3 are so placed that the piston begins to open them before it reaches the end of its power or working strokes and the air inlet ports 4 are so placed that the piston begins to open them shortly after the opening of the exhaust ports 3 is begun, both said ports being completely opened as the piston reaches the extreme end of the power or working strokes. The tier of ports 4 is for the low-pressure air. The ports 5 for the higher air pressure are preferably placed nearer the upper or head end of the cylinder than the lowerpressure ports and usually they are placed respectively above the lower-pressure air-inlet ports, as represented; usually, the higher pressure ports are so placed that the piston 2 at least begins to uncover them before it begins to uncover the exhaust ports 3, and usually so close to the cylinder head that they are uncovered in part at least before the pressure within they cylinder (during the power or working strokes) falls to equality with the pressure of the higher-pressure air supplied to them; in these latter respects however, the exact placement of these air inlet ports 5 will depend on the service or services to be performed by the air admitted through them, and

the pressure of this air, as will be understood. A receiver 6 is provided for the air-inlet ports 4, this being connected by an appropriate duct (indicated generally by the broken lines 8a in Fig. l) to the source 8 of air. Likewise a receiver 7 is provided for the air inlet ports 5, this being connected by an appropriate duct (indicated at 9) to the source 10 of air. Each of these'receivers 6 and '7 may be common to and supply the corresponding air-inlet ports of all or a number of the cylinders of the engine, as will be understood from common Diesel engine practise. An automatic or self-opening valve (or valves) 11, opening toward the interior of the cylinder, is provided for the air inlet ports 5. As here illustrated,

this automatic or self-opening valve or valvesV can conveniently have the form oflouvres or a series of light horizontally-pivoted plates or vanes opening toward the interior of the cylinder when the pressure within the receiver 7 is superior to `that within the cylinder, and closing against each other when the pressure backward through the ports 5 predominates. The air source 8 is so designed and constructed as to supply air at a .relatively low pressure or pressures, say a pressure about equal to some of the pressures now used in the simple low-pressure scavenging processes of Diesel engines; it may be higher however, or even lower than this; in general the pressure produced by this source 8 in any instance will 'be determined in accordance with the service desired of the air from this source, such as the amount of scavenging and charging to be done `:by the air, and whether some supercharging is desired when the air source 10 is out of operation as later referred to. The air source 10 is designed and constructed to deliver air at a higher Apressure than the source 8; and in general the pressure to be developed by this source 10 will be determined by the service desired of the air from it, such as the amount of scavenging and charging or supercharging.

Assuming both ail` sources 8 and 10 to be in operation, it will be recognized that the apparatus so far described embodies the scavenging and charging or supercharging process before referred to. As the piston 2 descends during each power or working stroke, the air-inlet ports 5 are iirst opened, thereafter the exhaust ports 3 are opened, and later the air-inlet ports 4 are opened. Just as soon as the pressure of the combustion gases within the cylinder has fallen below the relatively-high air pressure within the receiver 7, the automatic or self-opening valves 11 open and air from source 10 begins to enter through the ports 5; as the ports 4 are opened, air from source 8 enters through the ports 4, to join with air from the ports 5 in scavenging and charging the cylinder. As the piston 2 ascends on each compression stroke, the ports are closed and the air inows are discontinued in the reverse order.

The low-pressure source S however is capable of supplying the engine with all the scavenging and charging or supercharging air the engine may require at some degree of load or speed whereat the use of a single low-pressure compressor such as 8 is more economical than the use of the two compressors such as 8 and 10. This degree of load or speed will be less than the maximum, and in each instance the degree of load or speed for which the low-pressure source will be designed to satisfy these air requirements of the engine will be determined by the economics ci the particular situation, including convenience. Furthermore, it is by preference a centrifugal blower and its pressure-volume characteristic is represented by a curve which begins to droop when the range for which it is designed is exceeded; that is to say, the air pressure developed by this blower will decline if and as a greater volume of air (a greater rate of air flow) is permitted to come from it. The design of blowers of such a characteristic is well known. Moreover, such blower is so constructed and operated, and its pressure-volume characteristic is such, that it can supply all the scavenging and charging air (and also such supercharging air as may be needed or desired) throughout its selected range of low loads and speeds, so that having once taken over the air service of the engine to the exclusion oi blower or compressor 10, it can continue to supply the needs of the engine for scavenging and combustion air below and up to its designed limit, as, for example, the load or speed is or are further reduced.

Conveniently, the source l0 can be a centrifugal blower also, as illustrated, having the proper pressure characteristics. As representative of means for driving the two air sources whereby the higher-pressure source l0 can be discontinued from operation at will, that is to say, at the lesser engine loads or speeds, and restarted again at will, i. e., for the higher engine loads or speeds. I have shown the two blowers driven by individual electric motors 16 and 19, the former being ico ics

Lev-9,770

connected by the lines l`7 to the vsource ufr-curre-nt or supply lines 1B, and the motor 19 being connected to the same Isupply linesby Jthe'lines-'20, and the interposed manual switch 2l.

:es representative of arrangements whereby the lower-pressure blower 8 lcan deliver to they engine cylinder through the higher-pressure ypassages, as well as through -its'ownpassag-es, when this-air source alone is in'opcrat-ion (and alsoas generally representative of the -preferredarrangenient to this end) I have shown the common wall between the two receivers 6 andl pierced with a passageway 122 of adequate size, and van automatic or self-operating valve-therefor in the form of a light flap valve 23-hinged on `airis 24; when both sources 8 and 10 of -air are in operation, the superior pressure from source 1'() holds this valve closed over the passage 22, but when source 8 alone is in operation, air from this source will serve to open the iapand thus gain admittance to the air-inlet ports 5. Consideration of the matter will show that it is advantageous to permit the lower-pressure air to use the higherpressure air passages, as well ras its own passages, when the higher-pressure source is taken out of operation. Also Aas representative of lautomatic or self-operating valves 'for closing the `passage from the high-pressure receiver 7 to the highpressure source when the latter is out of operation, I have shown 'back seat 25 for the flap 23; when the latter opens passage 22 it bears on this valve seat 25 and thus prevents escape of air from receiver 'i through the (now stationary) blower l0.

The method of operation will be apparent from the foregoing. At the higher engine loads or speeds, both sources 8 and l0 are in operation (switch 21 being closed), and the scavenging and charging, or supercharging, is done as before described. At lower engine loads and speeds the higher-pressure air source l0 is held inoperative (by the opening of switch 21), and source 8 alone serves to supply scavenging and charging air through both tiers of ports 4 and 5, fiap valve 23 being held back against its seat 25, with or without some supercharging depending on the pressure of the air delivered by this source 8.

Usually it is desirable to direct the air from both tiers of ports somewhat toward the head end of the cylinder. This is done, preferably, by sloping ports 4 and 5 upwardly as appears in Fig. 2.

It will be understood from the foregoing that my invention is not limited to using air at only two dilferent pressures, and the claims which follow will be understood accordingly; however air at only two diiierent pressures seems to be adequate to satisfy present conditions. Obviously in general my invention is not limited to the exact operation and the constructions illustrated in the accompanying drawing and described in detail above. This will be apparent to the engineer without further description.

The following is claimed:

l. Means for scavenging, charging and supercharging a cylinder of a two-cycle internal combustion engine, comprising a source of low pressure air, a source of higher pressure air, a duct communicating with and receiving the air from the source of low pressuraa duct communicating with and receiving scavenging air from the source of higher pressure, a passage connecting said ducts, valve means to open and close said passage, valve means between the source of higher pressure and the high pressure duct, to open and close the communication between them, the cylinder having piston-controlled ports in its wail ccnnected to the low pressure duct and other piston controlled ports in its wall connected to the vhigher pressure duct, a valve or valves betweenthe vhigher pressure duct and ports, and meansfor placing the source et' higher pressure into and-out of operation.

2. In -a two-cycle internal combustion engine having piston-controlled exhaust and air inlet ports in the side Wall of a cylinder, separate sources for scavenging air at dierent pressures, means provi-ding passageways connecting said 'air sources to said air inlet port or ports, and means for discontinuing vand restarting one or more of said air sources which deliver air at a relatively high pressure, the remainder of said air sources remaining in operation, said passageways including a passageway connecting, when said relatively-high pressure source is out of action, other of said air sources to the air-inlet port or ports through whichvsaid higher-pressure source delivers when in action.

3. In a two-cycle internal ycombustion engine having a piston-controlled exhaust port and piston-controlled air-inlet ports, a source of scavenging air at arelatively Vlow pressure capable of supplying all the scavenging and charging air 'the engine requires at rsome degree of working load less than the maximum, means providing a passageway for air connecting said source to some lof said air-inlet ports, another `source of scavenging air at a higher pressure, means providing a passageway 'for air connecting the latter source to other 'of said ports, means for stopping the operation of and restarting said source of scavenging air at vthe higher pressure, the said source of lower pressure remaining in operation, and means for connecting said lower-pressure scavenging-air source to the said air-inlet port or ports of said higher-pressure source, so as to deliver air therethrough as well as through its own inlet port or ports, while the said higherpressure source is inoperative.

4. In a two-cycle internal combustion engine having a piston-controlled exhaust port and piston-controlled air-inlet ports, a source of scavenging air at a relatively low pressure connected to some of said air-inlet ports, another source of scavenging air at a higher pressure connected to other of said ports, means for stopping the operation of and restarting said source of scavenging air at the higher pressure, the said source of lower pressure remaining in operation, and a passage being provided leading from said scavenging-air source of lower pressures to the air inlet port or ports for said higher pressure scavenging-air, and an automatic self-operating valve to hold said passage closed while said higher-pressure source is in operation and opening said passage when said higher-pressure source is inoperative.

5. In a two-cycle internal combustion engine having a piston-controlled exhaust port and piston-controlled air-inlet ports, a source of scavenging air at a relatively low pressure connected /to some of said air-inlet ports, another source of scavenging air at a higher pressure connected to other of said air-inlet ports, means for stopping the operation of and restarting said source or' scavenging air at the higher pressure, the said source of lower pressure remaining in operation, a passage leading from said scavengingair source of lower pressure to the air-inlet port or ports for said higher-pressure scavenging-air,

said air-inlet port or ports for the air from said higher pressure source being located nearer the head end of the cylinder than the said air-inlet ports for the air from said lower pressure source, automatic self-operating valve means closing the said air-inlet port or ports for said higher-pressure scavenging-air when the cylinder pressure predominates, closing said passage when said higher-pressure source is operating, andclosing the connection to said higher-pressure source While the latter is out of operation.

6. The method of scavenging and charging a two-cycle internal combustion engine having piston-controlled exhaust and air-inlet ports, which consists in, at higher engine loads, supplying scavenging and charging air through said air-inlet ports at a plurality of different pressures, for a part of the time at least air at a plurality of different pressures being supplied simultaneously, and, at lower engine loads, supplying scavenging and charging air through the same air-inlet ports at a lesser number of pressures.

'7. The combination with a two-cycle internal combustion engine, of means connected to said engine for providing scavenging air therefor at a relatively high pressure, means independently connected to said engine for providing scavenging air therefor at lower pressures, said latter means being, at an engine load or speed less than maximum, capable of supplying scavenging air to the engine in adequate Volume at adequate pressure to meet the engine requirements, and means for discontinuing the operation of the irst mentioned means and restarting the same, the second mentioned means remaining in operation.

8. The combination with a two-cycle internal combustion engine having piston-controlled side exhaust and air-inlet ports, of a source of relatively high pressure air, a source of lower pressure air, said source of lower pressure being, at an engine load or speed less than maximum, capable of supplying air to the engine in adequate volume at adequate pressure to meet the engine requirements, each of said sources of air being connected to said air-inlet ports to supply scavenging air thereto, and means to discontinue the operation of said higher pressure source and restart it, the said lower-pressure source remaining in operation.

9. The combination with a two-cycle internal .combustion engine having piston-controlled side exhaust and air-inlet ports, of a source of relatively high pressure air connected to some of said air-inlet ports to supply air for scavenging, a ,source of air at a lower pressure, said source of lower pressure being, at an engine load or speed less than maximum, capable of supplying air to the engine in adequate volume at adequate pressure to meet the engine requirements, said lowerpressure source being connected to other of said air-inlet ports than that or those to which said higher pressure source is connected, a passage being provided for leading air from said lowerpressure source to said air-inlet port or ports to which said higher-pressure sources is connected, means for opening said passage when said higher-pressure source is inoperative and for holding said passage closed while` the higherpressure source is operative, and means for discontinuing the operation of said higher-pressure source and restarting it again, the said lowerpressure source remaining in operation.

EDWARD B. POLLISTER.

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